The pair, playing in the final group, both finished eight under alongside Ryan Palmer and Scotland's Russell Knox after a remarkable last hour at the Jack Nicklaus-designed PGA National in Palm Beach Gardens, Florida.

McIlroy had earned his place with a stunning approach to the last but faltered around the green when the hole was replayed for the play-off and it was Henley who prevailed with a birdie four.

McIlroy began the day 12 under par, two clear of his playing partner, but both his birdies on the front nine were immediately cancelled out by bogeys.

He dropped another shot at the ninth to leave himself 11 under and it closed up further on the back nine.

McIlroy dropped another at the 12th and followed a double-bogey at 16 - where he hit out of a bunker into the water - with another bogey to fall out of the lead altogether.

Henley had pitched in at 14 for a second successive birdie but gave both strokes back at the next when he dunked his tee shot in the water.

Palmer bogeyed the last to fall to eight under and was joined by Knox, the Scot's double-bogey six at the 14th proving costly - but the pair were able to watch in hope while keeping loose for a possible play-off.

At the 18th, though, McIlroy produced a moment of magic to set up the chance of a fairytale winning eagle.

The 24-year-old's second shot carried the water and bunker in front of the green and stopped almost dead, 20 feet from the pin.

Henley responded by duffing his pitch on, leaving himself a 60-foot birdie putt which he lagged to within five.

McIlroy's eagle putt trickled just by on the right and after he tapped in, Henley also holed out to make the play-off and he kept his nerve to make birdie while his rivals fell away.

Earlier, w orld number one Tiger Woods withdrew after 12 holes of his final round due to back pain. Woods shot 65 on Saturday to move into contention but was five over for his final round when he called it quits.

McIlroy told pgatour.com: "I didn't play well enough to deserve to win today. It's very disappointing. It was a perfect opportunity to win. No one was really coming at me.

"There's a few positives to take, but obviously it's going to be hard to get over because I had a great chance to win my first tournament of the season and I didn't.

"It's tough to take at the minute but I'll sleep it off tonight and get back at it."